Torque /physics related

Question

A see-saw is balanced on its

midpoint A 22.4 kg kid sits on the

left ,1.75 m from the axis. A

second kid sits on the other side.

1.22 m from the axis. What is the

mass of the second kid?

Can someone answer this thourghly?

Answer 1

Let the center of mass be at the origin.

R=0, M_A=22.4 kg, M_B=? kg, r_A=-1.75 m , r_B=+ 1.22 m

m_Ar_A + m_Br_B = (m_A+m_B)R

m_Ar_A + m_Br_B = 0

m_B = (-22.4*(-1.75))/(1.22)=32.13 kg